A communications network is any system or mechanism that provides for the exchange of information or data between participants. As used herein, the term “participant” refers to any device or mechanism that exchanges data with other devices or mechanisms over a communications medium. In some communications network arrangements, one of the participants is designated as a “master participant.” As used herein, the terms “master participant” and “master” are synonymous. The master participant performs one or more functions that are assigned to only the master participant and not to other participants. For example, a master participant may initiate and manage communications with other participants. As another example, the master participant may select a particular frequency hopping scheme to be used in the communications network.
In communications networks with a master participant, the other participants are conventionally referred to as “slave participants.” As used herein, the terms “slave participant” and “slave” are synonymous. Communications networks that use a master participant conventionally use only a single master participant, with any number of slave participants. Master participants are typically elected from available slave participants according to a selection or voting algorithm.
A frequency hopping (FH) protocol is an approach for wireless communications in a communications network that uses a frequency hopping signal transmission technique in which information or data is transmitted over a set of frequencies in a communications frequency band. A frequency hopping communications system is a system that uses a FH protocol. The order in which the communications network hops among the set of frequencies is known as the hopping sequence.
In contrast to FH systems, a non-frequency hopping (NFH) system is simply a communications system whose carrier does not hop over a set of frequencies. A typical NFH system may occupy a portion of the communications frequency band corresponding to several frequencies used by an FH system.
With some communications system approaches, such as the FH approach, the frequency band is broken up into separate frequencies, often referred to as “communications channels.” As used herein, the terms “communication channel” and “channel” are synonymous. For example, an FH system transmits data on one channel, hops to another channel in the hopping sequence to transmit more data, and continues by transmitting data on subsequent channels in the hopping sequence. The switching of frequencies may occur many times each second. The use of an FH protocol helps to reduce problems with interference from other communications systems and other interference sources. Frequency hopping also helps with fading of transmissions and power consumption and provides security for the transmission so that others may not intercept the data being transmitted because others do not know the hopping sequence.
An example of a frequency hopping protocol is the Institute of Electrical and Electronics Engineers (IEEE) 802.15.1 Wireless Personal Area Network Standard, which is based on the Bluetooth™ wireless personal area network (WPAN) technology from the Bluetooth Special Interest Group (SIG). The BLUETOOTH trademarks are owned by Bluetooth SIG, Inc., U.S.A. The Bluetooth protocol uses 79 individual randomly chosen frequency channels numbered from 0 to 78 and changes the frequencies 1600 times per second. Examples of NFH systems include the IEEE 802.11b Wireless Local Area Network (WLAN) and the IEEE 802.15.3 next-generation WPAN, both of which operate in the 2.4 GHz Industrial, Scientific, Medical (ISM) band, which is an unlicensed portion of the radio spectrum that may be used in most countries by anyone without a license.
Typically, the master of an FH communications system transmits at even-numbered timeslots on the hopping sequence and the slaves listen at those regular intervals. The master will address one slave (or all slaves in a “broadcast” mode), and the addressed slave responds back to the master at the next odd-numbered timeslot. A preamble, which is known to all the participants of the FH network, is used to identify the network and for the slaves to synchronize with the master. For example, in Bluetooth and IEEE 802.15.1, the known preamble is called the “channel access code.”
A common problem for communications systems is poor transmission quality of communications channels, also referred to as poor channel performance, which results in data transmission errors. For example, poor channel performance may increase the bit error rate (BER) or result in the loss of packets, leading to reduced transmission quality. As used herein, a “data packet” is a block of data used for transmissions in a packet-switched system, and the terms “data packet” and “packet” are synonymous.
A common source of poor channel performance is interference from other communications systems or other interference sources. Interference has a dynamic nature due to the use of devices at different times and locations, and as a result, eventually all channels of a communication system that uses multiple channels will experience some degree of interference at some time. Interference may change depending on when the communications systems use the band and the relative locations of the participants of each system to participants of other systems. Because the participants may be mobile, interference may vary depending on the movements of the participants of one system relative to the locations of participants of other systems. In addition, interference may arise from other sources resulting in a degradation of performance.
Another common source of poor channel performance is the coexistence problem that may arise between the communications systems that operate in the same frequency band. For example, while an FH communications system hops over the entire frequency band, an NFH communications system occupies separate parts of the frequency band. When the FH communications system hops over part of the frequency band occupied by an NFH communications system, there may be interference between the systems. Although the use of a FH protocol helps to lessen the interference problem because not all of the FH channels will interfere with other communications systems, there nevertheless remains interference on those channels that coincide with the NFH communications systems. An example of the interference situation is the coexistence problem between the frequency hopping IEEE 802.15.1 WPAN and the non-frequency hopping IEEE 802.11b Wireless Local Area Network (WLAN) because both share the 2.4 GHz ISM band.
One approach for managing poor channel performance is to increase the power used in the transmissions such that interference has less of an impact on the system transmitting at the increased power. However, in mobile applications, this increased power approach drains batteries used by the participants, and thus the required power increase may be impractical. Also, the increased power approach only benefits the system using the increased power and results in a bigger interference impact on other systems.
Other approaches for managing interference include retransmitting data that had errors in an original transmission and incorporating a form of redundancy into the transmission (e.g., by including multiple copies of some or all of the data) so that the participant receiving the data can identify and correct transmission errors. However, such approaches require additional resources to both identify the errors and then to correct the errors, such as by using additional transmissions or by using redundant data transmission approaches that decrease the amount of information that can be transmitted, which reduces the performance of the communications system.
Furthermore, using only a single master participant can have numerous drawbacks. In particular, if for any reason the master participant cannot perform its assigned functions, then the communications network will not function and the participants will not be able to communicate with each other. The master participant may not be able to perform their assigned functions for a variety of reasons. For example, in a wireless communications network with mobile participants, the master participant may move out of range of one or more slave participants, or vice versa. As another example, the master participant's power supply may drop below a minimum threshold or the master participant may otherwise fail. In any of these situations, the slave participants must first recognize that the master participant can no longer perform its assigned functions. Once the slave participants have made this determination, a new master participant must be selected from the available slave participants. Once the new master participant is selected, the functions assigned to the prior master participant must be assigned to the new master participant. Given that a master participant may fail at any time for a variety of reasons, either or both of these tasks may require a significant amount of time and computational resources and cause a significant disruption to the communications network.
Based on the need for wireless communications and the limitations in the conventional approaches, an approach for managing poor performance of communications channels and transferring management functions between participants that does not suffer from the limitations of the prior approaches is highly desirable.